ABSTRACT: The effects of competition rules on innovation can be very far reaching and may be seen as a hindrance to one of its foundational aims; increasing consumer welfare. The aim of this discussion is to provide the reader with sufficient background knowledge of unilateral refusal to supply pursuant to Article 102 TFEU. The piecemeal legal principles show the development of this murky area. Having set the scene, it will look at one of the more prominent cases in the area; the Commission decision against Microsoft. Law and economics overlap greatly, especially where competition policy is concerned and this discussion will highlight the ongoing legal and economic debates underlying the Microsoft decision. More recent developments in the area of unilateral refusal to supply will be highlighted followed by a comparative discussion on how this area is tackled in the United States with special emphasis on the Trinko decision.